Background: Though numerous studies have compared overground and treadmill walking there still exists a significant debate about whether the two modes of walking are equivalent. The present study provides a comprehensive evaluation of overground and treadmill walking at matched speeds and increasing treadmill speeds. Walking performance was compared in healthy adults, in people with stroke and between the groups. This is important to know because any differences may have implications for gait training in both groups. Methods: Ten healthy adults (50-73 years) and ten subjects with stroke (54-80 years) walked at their self-selected speed overground which was matched on a treadmill. Temporal parameters, angular kinematics and vertical ground reaction forces were recorded during walking once subjects were in steady state as determined from their heart rate and oxygen uptake, both of which were also recorded. Belt speed was then increased 10% and 20% above matched speed and steady state recordings obtained. Speed related adjustments were also evaluated and compared between the two groups of subjects. Results: For healthy adults, step, stride, and joint angular kinematics were similar for both modes of walking. Small reductions in double support time and decreased push-off force were evident on the treadmill. For subjects with stroke, step, stride, and stance times were longer when walking overground but the degree of symmetry was comparable for both surfaces. Kinematic data revealed interlimb asymmetry was more pronounced for all lower limb joint excursions during overground walking and vertical forces were higher. In comparison to healthy adults, stroke subjects walked with lower cadence, shorter strides, lower stance time, and smaller lower limb joint excursions than their healthy counterparts. When compared with overground walking the metabolic requirements of treadmill walking for healthy adults and subjects with stroke however were about higher by 23% and 15% respectively. All temporal-distance parameters, hip joint excursion, F1 and F2 forces and metabolic costs showed main effects of speed. An interaction between speed and group indicated that oxygen consumption increased at a greater rate in stroke than healthy subjects. Conclusions: The findings suggest that, although overground and treadmill gait patterns are similar for each group of subjects, people with stroke adopt a more symmetrical kinematic walking pattern on the treadmill that is maintained at faster belt speeds. Although there are differences in gait patterns between healthy and stroke subjects, both groups respond to the challenge of increased walking speed in the same way. One important difference is the abnormal elevation of energy demands associated with treadmill walking at faster speeds in stroke. Clinically, this warrants consideration as it may lead to premature fatigue and undesirable cardiorespiratory challenge in this group of individuals.